WHOIS IP Lookup
Look up registration details for any IPv4 address. Find network ownership, organization, country, CIDR block, and RIR information using the RDAP protocol. A free tool by IPv4Center.
What Is a WHOIS Lookup?
A WHOIS lookup retrieves registration and ownership information for an IP address or domain. This includes the organization that holds the IP block, the Regional Internet Registry (RIR) it belongs to, the network range (CIDR), country of registration, and current status. WHOIS data is essential for network administrators, security researchers, and anyone investigating IP address ownership. Our tool uses the modern RDAP (Registration Data Access Protocol), which is the successor to the traditional WHOIS protocol, providing more structured and reliable results.
How Does WHOIS Lookup Work?
When you enter an IP address, our tool queries the RDAP servers maintained by Regional Internet Registries (RIPE NCC, ARIN, APNIC, LACNIC, AFRINIC). RDAP returns structured JSON data about the IP block, including the network name, managing organization, country code, allocation status, and relevant dates. Unlike the legacy WHOIS text protocol, RDAP provides standardized, machine-readable responses with proper authentication and access control.
What Is WHOIS and How Does It Work?
WHOIS is a query-response protocol defined in RFC 3912 that provides registration information about internet resources including IP addresses, domain names, and autonomous system numbers. The protocol operates over TCP port 43 and returns human-readable text records from authoritative databases maintained by Regional Internet Registries (RIRs) and domain registrars.
Each of the five RIRs — RIPE NCC, ARIN, APNIC, LACNIC, and AFRINIC — maintains its own WHOIS database containing records for all IP allocations and assignments within its service region. When a WHOIS query is made, the system identifies the authoritative database based on the IP range and routes the request accordingly. Modern implementations use RDAP (RFC 7480–7484), which returns structured JSON over HTTPS instead of unformatted text.
A typical WHOIS response includes the network name (netname), organization handle, abuse contact, CIDR range, allocation status, creation and last-modified dates, and any associated route objects. For privacy-sensitive records, RIRs may redact personal data in compliance with GDPR and similar regulations while still providing operational contact information.
Understanding IP Address Ownership
IP address ownership is managed through a hierarchical allocation system overseen by IANA (Internet Assigned Numbers Authority) and distributed through five Regional Internet Registries. IANA allocates large blocks (typically /8) to RIRs, which then sub-allocate smaller blocks to Local Internet Registries (LIRs) and end users based on demonstrated need or transfer agreements.
The distinction between allocation and assignment is critical in the IP address ecosystem. An allocation is a block of addresses distributed to an LIR for the purpose of further assignment to its customers, while an assignment is a block given directly to an end user for use on their network infrastructure. Allocations carry redistribution rights; assignments do not.
As of 2026, all five RIRs have exhausted their free IPv4 pools, making the secondary market the primary mechanism for obtaining IPv4 address space. Ownership transfers must be recorded in the relevant RIR database, and WHOIS/RDAP queries remain the authoritative method for verifying current registration status before any transaction.
Frequently Asked Questions
WHOIS is a protocol for querying databases that store information about registered IP addresses and domain names. It helps identify who owns an IP block, which organization manages it, and which RIR region it belongs to. This information is crucial for network troubleshooting, abuse reporting, and due diligence in IP address transactions.
RDAP (Registration Data Access Protocol) is the modern replacement for WHOIS. While WHOIS returns unstructured text, RDAP provides structured JSON responses, supports HTTPS, has built-in access control, and is standardized across all RIRs. Our tool uses RDAP for more accurate and reliable results.
You can look up any publicly routable IPv4 address. Private IP ranges (10.x.x.x, 172.16-31.x.x, 192.168.x.x) and reserved ranges will not return useful WHOIS data as they are not registered in public databases.
The status field indicates the current allocation state of the IP block. Common statuses include "active" (currently in use), "allocated" (assigned by an RIR to an organization), and "reserved" (set aside for specific purposes). The status helps understand whether an IP block is actively being used and how it was assigned.
WHOIS data is sourced directly from the Regional Internet Registries (RIRs) and is generally accurate. However, some records may be outdated if the registrant has not updated their information. For IPv4 transfer due diligence, we recommend cross-referencing WHOIS data with BGP routing data and blacklist checks.
Before purchasing IPv4 addresses, a WHOIS lookup helps verify the seller's ownership, confirm the correct RIR region, check the block size and range, and identify any potential issues. It is an essential step in the due diligence process for IPv4 transactions on our marketplace.